I've seen cases when the ESC key stroke in "all notifications have disappeared"
closes the very dialog that we'll be looking for in the next step
("I am proposed to install an incremental upgrade to…"). I suspect
this never happened before because the Upgrader took longer to start,
so optimizing it introduced this race condition.

In these scenarios, I doubt that closing notifications is important: the
aforementioned zenity dialog is always displayed in the center of the screen and
there's little change a notification hides it.

The Unsafe Browser needs a DNS resolver configured so we need to plug
the network first.

While working on the test suite, it took me a while to figure out why the exit
code, stdout, and stderr of a failed command was not in the Journal. It turns
out that it's because our test suite does not properly close the zenity dialog
that we display before printing the more detailed debugging info to STDERR and
thus to the Journal, which makes debugging via the test suite impractical.

A user could be affected in a similar way: before this commit, when we told them
"For debugging information, execute the following command: sudo
tails-debugging-info", the info we were referring was actually not in the
Journal yet.

Given the test UDFs we're using, an initially installed 2.0~test
will be upgraded to 2.2~test.

Move the Upgrader's trusted keyring to tails-upgrade-frontend's $HOME and make it writable by that user (refs: #15279)

This will be needed in order to refresh our signing key before checking
for upgrades.

generate-languages-list is not meant to be used directly
by anyone, so let's move it out of the way.
auto/build has auto/scripts/ in its $PATH.

tails-iuk-check-upgrade-description-file uses Data::Dumper::Concise.

The RM also needs them.

It was only needed for extracting nested archives.
Now that we can simply mount the IUK, we don't use this anymore.

Copied from the feature/15281-single-squashfs-diff branch in iuk.git
at commit abe82504d03bacbc3e803c9a9d53d4f359488239.

On top of that:

 - Removed PO files as translations will be managed with tails.git's system
 - Removed obsolete PO and Git integration
 - Moved most dependency management from dist.ini to our "release" doc

Doing this by hand one more time now, and once again soon for IUK v2 +
overlayfs, was not particularly appealing.

This is about verifying that the upgrade was correctly applied,
not about the Unsafe Browser.

… as suggested by anonym when he implemented this initially :)

This brings back 2763439d:
https://redmine.tails.boum.org/code/issues/15286#note-8

Adapt incremental upgrade manual test for the "one single SquashFS diff" upgrade scheme (Closes: #15285)